This randomized clinical effectiveness trial will test the ability of a pharmacist intervention to improve the outcomes of treatment of depressive disorders in primary care. Numerous treatments are available; however, all require compliance to be effective. Approximately 30% of depressed primary care patients stop using antidepressant medications within the first month of treatment, while only 40% reach the recommended therapeutic dosage of antidepressant medication. Participation in care by clinical pharmacists has been proposed as a way to ensure the safe and effective use of drugs and to improve compliance. However, their specific clinical and economic contributions to the care of patients with depressive disorders are unknown. This study will evaluate the impact of standardized pharmacist interventions on the clinical, therapeutic, health status and financial outcomes of care, and on patient satisfaction with care. Specifically, we aim to (1) Compare, between the intervention and control group: a) the optimality of drug therapy for depressive disorders as defined by AHCPR guidelines; b) patient compliance with and knowledge of antidepressant medications; c) the number of drug-related problems; d) the resolution of clinical symptoms of depression and health status outcomes; and e) patient satisfaction; (2) Estimate the economic consequences (e.g., utilization of health resources, work functioning) and cost-effectiveness of the intervention. Consecutive patients (n=27,000) from 3 primary care practice settings will be screened. Patients meeting DSM-IV criteria for major depression or dysthymia (n=710), based on a validated two-stage screening process, will be randomized to either an intervention or control group. Four pharmacists will participate in the primary care physicians' (PCP) care of each patient in the intervention group by: conducting an initial evaluation; following a standardized protocol to monitor drug therapy; assessing compliance and recommending strategies to correct non-compliant behavior, and educating and counseling patients about drug use. Patients in the control group will receive usual care from their PCP. All groups will be assessed at 3, 6, 12, and 18 months. By doing this study, we hope to elucidate whether participation of a clinical pharmacist in primary care treatment of depression improves the process of patient care, improves health outcomes and patient satisfaction, and decreases the economic costs of depression.